In gas analysis, sensors are in use for determining the concentration of gases, more generally for detecting risks when working with microwaves, for smoke and fire detection, and the like, which consist of sensor elements in the form of semiconductors or specially processed resistors varying their resistance value in response to the value to be measured, i.e. especially in response to the gas concentration to be measured.
In the case of these known methods for processing measured values, i.e. especially when semiconductor sensors are used as measure for the gas concentration to be measured--and this is the application which will be described in more detail below because it is the preferred application of the present invention although the latter is not restricted to it--the indication of the gas concentration measured is derived from the varying resistance value which will be described hereafter by RS. However, such a sensor which varies its resistance value in response to the value to be measured is not capable of starting at a resistance value of zero when the concentration is equal to zero, for example; instead, the respective semiconductor sensor has a basic resistance value Ro which will initially be regarded hereafter as a constant value, but this only with respect to the gas concentration to be measured, as this basic resistance is in fact dependent on many other factors and may be subject to foreign influences external to the measurement proper.
So, the value normally measured is the sum of the basic resistance Ro plus the resistance portion .DELTA.RS which leads to the aggregate resistance RS.
The basic resistance value Ro may vary for certain sensor types, due to production reasons, between 5 kOhm and 15 kOhm and may, in addition to these wide variations, be dependent on the existing air humidity, angle and velocity of flow, aging phenomena, long-term stability and may also, under certain circumstances, be heavily influenced by temperature changes. When evaluating measurements taken, on the basis of the total resistance value assumed at any time by the semiconductor sensor, for example when measuring varying gas concentrations, these parameters will be contained in the results of the measurement as measuring errors or must be corrected and considered (later) by troublesome processes. To this effect, it will frequently be necessary to determine at least the temperature prevailing at the place of measurement so that it can be considered in evaluating the measured resistance values.
Now, it is the object of the present invention to provide a method and a device for processing measured values where any additional factors influencing the values determined by a sensor which varies its resistance value are minimized or even completely eliminated.